The present invention relates to a method of counting the number of passers-by, that is, a method of automatically counting the number of persons who come in and go away from department stores, movie theaters, concert halls and various meeting places.
As a method of counting the number of passers-by in a predetermined place, conventionally, there have been proposed a method utilizing optical detecting means, a method utilizing an infrared sensor, and a method utilizing a supersonic sensor and the like. However, these methods have such a drawback that the counting accuracy is reduced in a case that a plurality of persons who pass in a group is to be measured.
Accordingly, the Japanese patent application Serial No. 330921/90 entitled "Method of Counting the Number of Passers-by" and filed by the applicant of the present invention on Nov. 30, 1990, discloses an invention in which a plurality of ultrasonic transmitters/receivers (sensors) are juxtaposed in two files relatively adjacent to one another above a passage in a direction traversing the passage in such a manner that the height of an object to be measured which passes under the sensors is calculated from the time of arrival of reflected waves of the ultrasonic waves and the top (head) of the measured object is detected from changing states of the height data measured by the individual sensors in a lateral direction (a passage traversing direction) to count the number of passers-by, thereby to increase the counting accuracy.
However, in the above mentioned prior art, the head top is calculated from the changing state of the height data in the lateral direction upon each scanning operation, so that the individual sensor should be installed relatively close to one another, which induces an increase in cost of the apparatus embodying this method.
The present invention has been contemplated in view of the above-mentioned drawback associated with the prior art.